I have an HTC Evo. It's a wonderful little device, and I use it constantly. However, I'm shoveling money into Sprint's coffers at the rate of $70/month. That's eight hundred and forty dollars a year!
I know I should cancel it, but it's hard. I use it all the time, mostly for web browsing and ebook reading.
If I cancel my plan, I would keep the device and just use it with wi-fi. The only problem is, wi-fi is not available everywhere. I use Google Maps fairly often to look up directions. I would miss this a lot.
For a phone, I'd probably just get a T-Mobile prepaid plan for $100/year (actually it's less than that after the first year). Between the landline at my house, and the desk phone at my job, I don't need to use a mobile phone for talking very often.
Please, Mustachians, tell me why I should cancel my phone. The main thing I'm worried about is not being able to look up directions when I'm on the road (or on my bike).